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https://issues.apache.org/jira/browse/HADOOP-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473279
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Hairong Kuang commented on HADOOP-972:
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The attached patch has a minor modification to the proposal. NetworkTopology
adds one chooseRandom method. When the scope starts with ~, it means to choose
a datanode excluding from scope; otherwise, it means to choose a random data
node from scope.
> Improve the rack-aware replica placement performance
> ----------------------------------------------------
>
> Key: HADOOP-972
> URL: https://issues.apache.org/jira/browse/HADOOP-972
> Project: Hadoop
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.11.0
> Reporter: Hairong Kuang
> Assigned To: Hairong Kuang
> Fix For: 0.12.0
>
> Attachments: rack_performance.patch
>
>
> This issue aims to improve the rack-aware replica placement performance. A
> major idea is to avoid constructing lists of possible targets for random
> selection in chooseTarget, which currently needs interating all
> DatanodeDescriptors. I plan to change the NetworkTopology data structure as
> follow:
> 1. each InnerNode stores its childrens as a list;
> 2. each InnerNode adds a new field numberOfLeaves the total number of leaves
> (i.e. data nodes) in its subtree.
> NetworkTopology will support two new methods:
> 1. DatanodeDescriptor chooseRandom( String scope): it randomly choose one
> leave from scope.
> 2. DatanodeDescriptor chooseRandomExclude(String excludedScope): it randomly
> choose one leave from ~scope
> In addition, Issue 971 will also help improve the performance of the
> rack-aware DFS patch.
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